The present invention relates to a needle selection device in knitting, sock- and stocking-making machines and the like.
Devices for the selection of the needles in knitting machines are known. In particular, in circular machines, said devices generally use selectors arranged below the needles in the grooves defined on the lateral surface of the needle cylinder. The selectors are provided, on their side facing towards the outside of the needle cylinder, with at least one heel and are controllably movable from an extracted position, in which said heel protrudes from the related groove to engage with selection cams arranged around the needle cylinder, to a sunk position, in which the heel of the selector is completely accommodated into the related groove so as to not engage with the selection cams. These selection cams define guide paths for the heel of the selector engaged therewith when the selection cams are caused to rotate relatively to the needle cylinder. By virtue of the movement of the selector heel along the paths of the selection cams, the selector undergoes a longitudinal shift in the related groove which causes it to push the overlying needle to selectively engage with its heel within adapted paths defined by needle cams rigid with the selection cams so as to perform the desired knitting.
If it is desired to exclude one or more needles from the knitting, it is sufficient to move or retain the related selector or selectors in the sunk position. As is apparent, the choice of the needles to be operated is determined by the choice of the selectors which are brought or kept in the extraction position. To effect this choice, each selector is provided, on the side facing towards the outside of the needle cylinder, with a plurality of heels which are engaged or not by adapted levers or blades to push them in the sunk position or keep them in the extraction position.
Selection devices are known which use a stack of levers, superimposed and oscillable by means of electromagnetic actuators from an operative position, in which one of their ends is placed at the level of one of the heels of the selector to push it in sunk position, to an inoperative position, in which the end of the lever is in an intermediate position between the heels of the selectors so as to not interfere therewith and therefore keep the selectors in extraction position.
Mechanical devices are also known, termed drawing drums, which provide the same conditions by moving, by means of pins protruding according to a preset arrangement on a rotating cylinder, the levers towards or away from the axis of the needle cylinder.
Similar selection devices are also used for the selection of the dial needles in circular knitting machines of the type with cylinder and dial.
In order to obtain an accurate selection, or to actuate a restricted number of selectors differently from the contiguous selectors, it is necessary to provide selectors with a high number of heels, therefore a high number of levers. This fact in turn entails the problem of arranging a high number of electromagnetic actuators or of equivalent devices proximate to the needle cylinder.
Since the selection must be effected in a restricted region, it is necessary to reconcile the opposite requirements of reduced dimensions and of high number of selection actuators to achieve an individual selection of the needles.
Another problem found in known selection devices is that of the wear due to the high number of actuation cycles of said devices caused by the high number of elements in mutual contact.